The use of NPPV for treatment of SDB such as Obstructive Sleep Apnea (OSA) was pioneered by Sullivan (see U.S. Pat. No. 4,944,310). Apparatus for the treatment of SDB involves a blower which delivers a supply of air at positive pressure to a patient interface via a conduit. The patient interface may take several forms, such as a nasal mask assembly and a nasal and mouth mask assembly. Patients typically wear a mask assembly while sleeping to receive the NPPV therapy.
Mask assemblies typically comprise a rigid shell or frame and a soft face-contacting cushion. The cushion spaces the frame away from the patient's face. The frame and cushion define a cavity which receives the nose or nose and mouth. The frame and cushion are held in position on the patient's face by a headgear assembly. The headgear assembly typically comprises an arrangement of straps which pass along both sides of the patient's face to the back or crown of the patient's head.
U.S. Pat. No. 5,243,971 (Sullivan and Bruderer) describes a nasal mask assembly for Continuous Positive Airway Pressure (CPAP) having a ballooning/molding seal that conforms with the patient's nose and facial contours. The mask assembly has a face-contacting portion mounted to a shell which is sized and shaped to overfit the nose region of the patient. The face-contacting portion is in the form of a distendable membrane which is molded from an elastic plastic material. The distendable membrane and the shell together define a chamber. Pressurized gas admitted to the chamber causes the membrane to distend outwardly from the patient's face. The contents of this patent are hereby incorporated by reference.
U.S. Pat. No. 6,112,746 (Kwok et al.) describes a nasal mask assembly and a mask cushion therefor. The contents of this patent are hereby incorporated by reference. The cushion comprises a substantially triangularly-shaped frame from which extends a membrane. The frame has an edge by which the cushion is affixed to a mask body. The membrane has an aperture into which the patient's nose is received. The membrane is spaced away from the rim of the frame, and its outer surface is of substantially the same shape as the rim.
The cushion of a patient interface can play a key role in the comfort and effectiveness of therapy. There is considerable variation in facial size and shape which can mean that a mask designed for one type of face may not be suitable for another. For example, an Asian-type nose tends to have a lower nasal bridge whereas a Caucasian-type nose has a higher nasal bridge. Using the wrong cushion can lead to excessive leak and discomfort. While creating customized cushions for every patient may solve some fitting issues, customized masks are very expensive. Thus, manufacturers seek to develop cushions which provide a comfortable and effective seal for a range of facial sizes and shapes.